ABSTRACT
When I was a student I remember attending a lecture about the human visual system. Midway through the lecture a visiting professor stood and walked to the podium. Addressing the speaker he said, “Look, I can see, I’ve walked up here, what more is there to know?” This was a profoundly ignorant statement which totally failed to appreciate the scientific challenge posed by the study of perception—in this case the visual system. The things around us do not automatically indicate to us what they are; our perception of the world is built up by internal processes which operate on an initial input that is far removed from what our sense organs initially register. Vision, for example, begins with a two-dimensional image on the retina but ends up as a three-dimensional scene in which there is depth, colour, movement, and so on. Similarly, hearing begins with the mechanical stimulation of cochlea hair cells by sound waves but what we hear is sufficient to allow us to appreciate the complex sounds of continuous speech.
